It has become commonplace to see radio transmission apparatuses (hereinafter, described as slave devices) not equipped with a receiving function such as a switch with an added radio signal transmission function being arranged at various locations of a production line or the like and, based on radio signals from the respective slave devices, a single radio reception apparatus (hereinafter, described as a master device) managing states of the various locations.
When constructing a unidirectional radio communication system in which unidirectional radio communication is performed from a plurality of slave devices to a master device such as that described above, while a position of each device is determined so that communication between each slave device and the master device can be carried out in a favorable manner, there may be cases where, after operation of the unidirectional radio communication system is started, an obstacle on a communication path causes radio field strength reaching the master device to drop excessively and, as a result, radio communication fails (the master device becomes incapable of receiving radio signals). In addition, there may be cases where radio communication fails due to a radio wave collision (a collision between radio signals from a plurality of slave devices or a collision between a radio signal from a slave device and a radio wave from another apparatus).
Existing unidirectional radio communication systems are not equipped with a function for notifying a user as to whether a drop in radio field strength due to an obstacle or a radio wave collision is a factor in radio communication failure. Therefore, in order to restore a unidirectional radio communication system in which a communication failure (a radio communication failure) has occurred to a state where radio communication can be performed normally, various tests for specifying a factor of the radio communication failure must be performed.
As long as bidirectional radio communication is concerned, various techniques (for example, PTL1) are developed for the purpose of notifying a user of a factor preventing radio communication from being performed. However, techniques related to bidirectional radio communication cannot be applied to unidirectional radio communication systems in which radio communication cannot be performed from a master device to slave devices.    PTL1: Japanese Patent Application Laid-open No. 2016-15652